why the atomic size of the inert gases are compartively larger than the halogens?
 

Dear student,

In a period, as we move from left to right the atomic radius decreases.

Noble gases which are at the end of each period, are expected to have smallest radii, but they have comparatively larger atomic radii. This is due to the reason that in case of inert gases, the outer shell is complete and it has hence maximum electronic repulsion.
Hence, their atomic size increases due to maximum repulsion between nucleus and valence electrons. 
Moreover in case of inert gases, the atomic size is expressed in terms of Vanderwaal’s radius because, noble gases do not form covalent bonds  while other form covalent bonds and hence their atomic radii is expressed in covalent radius. Thus as, Vanderwaal’s radius is greater than covalent radius, the atomic size of noble gases is larger than other elements of same period.

Keep asking!
Regards

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